Rubber composition and pneumatic tire

ABSTRACT

There is disclosed a vulcanizable rubber composition comprising:
         (A) a functionalized elastomer comprising the reaction product of a living anionic elastomeric polymer and
 
a polymerization terminator of formula I
       

                         
where R 1 , R 2  and R 3  are independently C1 to C8 alkyl or C1 to C8 alkoxy, with the proviso that at least two of R 1 , R 2  and R 3  are C1 to C8 alkoxy; R 4  is C1 to C8 alkyl; Si is silicon; S is sulfur; and Z is R 5  or of formula II
 
                         
where R 5  is alkyl, aryl, alkylaryl or arylalkyl;
         (B) a polymeric amine comprising a primary amine functionality; and   (C) an aromatic carboxylic acid or aromatic acid anhydride.

BACKGROUND OF THE INVENTION

Metals from Groups I and II of the periodic table are commonly used to initiate the polymerization of monomers into polymers. For example, lithium, barium, magnesium, sodium, and potassium are metals that are frequently utilized in such polymerizations. Initiator systems of this type are of commercial importance because they can be used to produce stereo regulated polymers. For instance, lithium initiators can be utilized to initiate the anionic polymerization of isoprene into synthetic polyisoprene rubber or to initiate the polymerization of 1,3-butadiene into polybutadiene rubber having the desired microstructure.

The polymers formed in such polymerizations have the metal used to initiate the polymerization at the growing end of their polymer chains and are sometimes referred to as living polymers. They are referred to as living polymers because their polymer chains which contain the terminal metal initiator continue to grow or live until all of the available monomer is exhausted. Polymers that are prepared by utilizing such metal initiators normally have structures which are essentially linear and normally do not contain appreciable amounts of branching.

Rubbery polymers made by living polymerization techniques are typically compounded with sulfur, accelerators, antidegradants, a filler, such as carbon black, silica or starch, and other desired rubber chemicals and are then subsequently vulcanized or cured into the form of a useful article, such as a tire or a power transmission belt. It has been established that the physical properties of such cured rubbers depend upon the degree to which the filler is homogeneously dispersed throughout the rubber. This is in turn related to the level of affinity that filler has for the particular rubbery polymer. This can be of practical importance in improving the physical characteristics of rubber articles which are made utilizing such rubber compositions. For example, the rolling resistance and traction characteristics of tires can be improved by improving the affinity of carbon black and/or silica to the rubbery polymer utilized therein. Therefore, it would be highly desirable to improve the affinity of a given rubbery polymer for fillers, such as carbon black and silica.

In tire tread formulations, better interaction between the filler and the rubbery polymer results in lower hysteresis and consequently tires made with such rubber formulations have lower rolling resistance. Low tan delta values at 60° C. are indicative of low hysteresis and consequently tires made utilizing such rubber formulations with low tan delta values at 60° C. normally exhibit lower rolling resistance. Better interaction between the filler and the rubbery polymer in tire tread formulations also typically results higher tan delta values at 0° C. which is indicative of better traction characteristics.

The interaction between rubber and carbon black has been attributed to a combination of physical absorption (van der Waals force) and chemisorption between the oxygen containing functional groups on the carbon black surface and the rubber (see D. Rivin, J. Aron, and A. Medalia, Rubber Chem. & Technol. 41, 330 (1968) and A. Gessler, W. Hess, and A Medalia, Plast. Rubber Process, 3, 141 (1968)). Various other chemical modification techniques, especially for styrene-butadiene rubber made by solution polymerization (S-SBR), have also been described for reducing hysteresis loss by improving polymer-filler interactions. In one of these techniques, the solution rubber chain end is modified with aminobenzophenone. This greatly improves the interaction between the polymer and the oxygen-containing groups on the carbon black surface (see N. Nagata, Nippon Gomu Kyokaishi, 62, 630 (1989)). Tin coupling of anionic solution polymers is another commonly used chain end modification method that aids polymer-filler interaction supposedly through increased reaction with the quinone groups on the carbon black surface. The effect of this interaction is to reduce the aggregation between carbon black particles which in turn, improves dispersion and ultimately reduces hysteresis.

SUMMARY OF THE INVENTION

The subject invention provides a low cost means for the end-group functionalization of rubbery living polymers to improve their affinity for fillers, such as carbon black and/or silica. Such functionalized polymers can be beneficially used in manufacturing tires and other rubber products where improved polymer/filler interaction is desirable. In tire tread compounds this can result in lower polymer hysteresis which in turn can provide a lower level of tire rolling resistance.

The present invention more specifically is directed to a vulcanizable rubber composition comprising:

(A) a functionalized elastomer comprising the reaction product of a living anionic elastomeric polymer and

a polymerization terminator of formula I

where R¹, R² and R³ are independently C1 to C8 alkyl or C1 to C8 alkoxy, with the proviso that at least two of R¹, R² and R³ are C1 to C8 alkoxy; R⁴ is C1 to C8 alkyl; Si is silicon; S is sulfur; and Z is R⁵ or of formula II

where R⁵ is alkyl, aryl, alkylaryl or arylalkyl;

(B) a polymeric amine comprising a primary amine functionality; and

(C) an aromatic carboxylic acid or aromatic acid anhydride.

The invention is further directed to a pneumatic tire comprising the rubber composition.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a graph of rolling resistance index for several rubber samples.

DETAILED DESCRIPTION OF THE INVENTION

There is disclosed a vulcanizable rubber composition comprising a functionalized elastomer comprising:

(A) a functionalized elastomer comprising the reaction product of a living anionic elastomeric polymer and

a polymerization terminator of formula I

where R¹, R² and R³ are independently C1 to C8 alkyl or C1 to C8 alkoxy, with the proviso that at least two of R¹, R² and R³ are C1 to C8 alkoxy; R⁴ is C1 to C8 alkyl; Si is silicon; S is sulfur; and Z is R⁵ or of formula II

where R⁵ is alkyl, aryl, alkylaryl or arylalkyl;

(B) a polymeric amine comprising a primary amine functionality; and

(C) an aromatic carboxylic acid or aromatic acid anhydride.

There is further disclosed a pneumatic tire comprising the rubber composition.

The subject invention provides a means for the end-group functionalization of rubbery living polymers to improve their affinity for fillers, such as carbon black and/or silica. The process of the present invention can be used to functionalize any living polymer which is terminated with a metal of group I or II of the periodic table. These polymers can be produced utilizing techniques that are well known to persons skilled in the art. The metal terminated rubbery polymers that can be functionalized with a terminator of formula I in accordance with this invention can be made utilizing monofunctional initiators having the general structural formula P-M, wherein P represents a polymer chain and wherein M represents a metal of group I or II. The metal initiators utilized in the synthesis of such metal terminated polymers can also be multifunctional organometallic compounds. For instance, difunctional organometallic compounds can be utilized to initiate such polymerizations. The utilization of such difunctional organometallic compounds as initiators generally results in the formation of polymers having the general structural formula M-P-M, wherein P represents a polymer chain and wherein M represents a metal of group I or II. Such polymers which are terminated at both of their chain ends with a metal from group I or II also can be reacted with terminator of formula Ito functionalize both of their chain ends. It is believed that utilizing difunctional initiators so that both ends of the polymers chain can be functionalized with the terminator of formula I can further improve interaction with fillers, such as carbon black and silica.

The initiator used to initiate the polymerization employed in synthesizing the living rubbery polymer that is functionalized in accordance with this invention is typically selected from the group consisting of barium, lithium, magnesium, sodium, and potassium. Lithium and magnesium are the metals that are most commonly utilized in the synthesis of such metal terminated polymers (living polymers). Normally, lithium initiators are more preferred.

Organolithium compounds are the preferred initiators for utilization in such polymerizations. The organolithium compounds which are utilized as initiators are normally organo monolithium compounds. The organolithium compounds which are preferred as initiators are monofunctional compounds which can be represented by the formula: R-Li, wherein R represents a hydrocarbyl radical containing from 1 to about 20 carbon atoms. Generally, such monofunctional organolithium compounds will contain from 1 to about 10 carbon atoms. Some representative examples of preferred organolithium compounds include butyllithium, secbutyllithium, n-hexyllithium, n-octyllithium, tertoctyllithium, n-decyllithium, phenyllithium, 1-naphthyllithium, 4-butylphenyllithium, p-tolyllithium, 4-phenylbutyllithium, cyclohexyllithium, 4-butylcyclohexyllithium, and 4-cyclohexylbutyllithium. Secondary-butyllithium is a highly preferred organolithium initiator. Very finely divided lithium having an average particle diameter of less than 2 microns can also be employed as the initiator for the synthesis of living rubbery polymers that can be functionalized with a terminator of formula I in accordance with this invention. U.S. Pat. No. 4,048,420, which is incorporated herein by reference in its entirety, describes the synthesis of lithium terminated living polymers utilizing finely divided lithium as the initiator. Lithium amides can also be used as the initiator in the synthesis of living polydiene rubbers (see U.S. Pat. No. 4,935,471 the teaching of which are incorporated herein by reference with respect to lithium amides that can be used as initiators in the synthesis of living rubbery polymer).

The amount of organolithium initiator utilized will vary depending upon the molecular weight which is desired for the rubbery polymer being synthesized as well as the precise polymerization temperature which will be employed. The precise amount of organolithium compound required to produce a polymer of a desired molecular weight can be easily ascertained by persons skilled in the art. However, as a general rule from 0.01 to 1 phm (parts per 100 parts by weight of monomer) of an organolithium initiator will be utilized. In most cases, from 0.01 to 0.1 phm of an organolithium initiator will be utilized with it being preferred to utilize 0.025 to 0.07 phm of the organolithium initiator.

Many types of unsaturated monomers which contain carbon-carbon double bonds can be polymerized into polymers using such metal catalysts. Elastomeric or rubbery polymers can be synthesized by polymerizing diene monomers utilizing this type of metal initiator system. The diene monomers that can be polymerized into synthetic rubbery polymers can be either conjugated or nonconjugated diolefins. Conjugated diolefin monomers containing from 4 to 8 carbon atoms are generally preferred. Vinyl-substituted aromatic monomers can also be copolymerized with one or more diene monomers into rubbery polymers, for example styrene-butadiene rubber (SBR). Some representative examples of conjugated diene monomers that can be polymerized into rubbery polymers include 1,3-butadiene, isoprene, 1,3-pentadiene, 2,3-dimethyl-1,3-butadiene, 2-methyl1,3-pentadiene, 2,3-dimethyl-1,3-pentadiene, 2-phenyl-1,3-butadiene, and 4,5-diethyl-1,3-octadiene. Some representative examples of vinyl-substituted aromatic monomers that can be utilized in the synthesis of rubbery polymers include styrene, 1-vinylnapthalene, 3-methylstyrene, 3,5-diethylstyrene, 4-propylstyrene, 2,4,6-trimethylstyrene, 4-dodecylstyrene, 3-methyl-5-normal-hexylstyrene, 4-phenylstyrene, 2-ethyl-4-benzylstyrene, 3,5-diphenylstyrene, 2,3,4,5-tetraethylstyrene, 3-ethyl-1-vinylnapthalene, 6-isopropyl-1-vinylnapthalene, 6-cyclohexyl-1-vinylnapthalene, 7-dodecyl-2-vinylnapthalene, α-methylstyrene, and the like.

The metal terminated rubbery polymers that are functionalized with a terminator of formula I in accordance with this invention are generally prepared by solution polymerizations that utilize inert organic solvents, such as saturated aliphatic hydrocarbons, aromatic hydrocarbons, or ethers. The solvents used in such solution polymerizations will normally contain from about 4 to about 10 carbon atoms per molecule and will be liquids under the conditions of the polymerization. Some representative examples of suitable organic solvents include pentane, isooctane, cyclohexane, normal-hexane, benzene, toluene, xylene, ethylbenzene, tetrahydrofuran, and the like, alone or in admixture. For instance, the solvent can be a mixture of different hexane isomers. Such solution polymerizations result in the formation of a polymer cement (a highly viscous solution of the polymer).

The metal terminated living rubbery polymers utilized in the practice of this invention can be of virtually any molecular weight. However, the number average molecular weight of the living rubbery polymer will typically be within the range of about 50,000 to about 500,000. It is more typical for such living rubbery polymers to have number average molecular weights within the range of 100,000 to 250,000.

The metal terminated living rubbery polymer functionalized with a terminator of formula I can be made following the procedures of US Publication 2013/0131263, fully incorporated herein by reference. As disclosed therein, suitable functionalized terminators of formula I include but are not limited to S-benzyl-S′-triethoxysilylpropyltrithiocarbonate:

The functionalized polymer may be compounded into a rubber composition.

The rubber composition further includes a polymeric amine, where the polymeric amine has a primary amine functionality. Suitable polymeric amines include but are not limited to polyethyleneimine, polypropyleneimine, and polyoxyalkylene amines

In one embodiment, the polymeric amine is a polyethyleneimine In one embodiment, the polyethyleneimine has an average molecular weight of 800 to 2000000, preferably 1000 to 20000, more preferably 2000 to 4000. Suitable polyethyleneimine is available commercially as Lupasol from BASF.

In one embodiment, the polymeric amine is a polyoxyalkylene amine. The polyoxyalkylene amine can include a polyoxyalkylene monoamine, diamine, triamine, or combinations thereof. These compounds are defined by an amino group attached to a terminus of a polyether backbone and, thus, are considered polyether amines. The amino group is a primary amino group. Depending upon whether the polyoxyalkylene amine is a mono-, di-, or triamine, each compound can contain, respectively, one, two, or three amino groups, e.g. primary amino groups, with each group being attached to the terminus of a polyether backbone. Accordingly, one or more polyether backbones may be necessary to accommodate the number of terminal amino groups. Further description of polyoxyalkylene amines and their use is as disclosed in U.S. Pat. No. 7,714,051, fully incorporated herein by reference. Suitable polyoxyalkylene amines include polyoxyalkylene mono-, di-, and triamines commercially available from Huntsman Chemical of The Woodlands, Tex. and sold under the tradename JEFFAMINE®.

Polymeric amine may be used in an amount ranging from 0.1 to 10 phr. In one embodiment, the polymeric amine is used in an amount ranging from 0.1 to 5 phr. In one embodiment, the polymeric amine is used in an amount ranging from 0.1 to 2 phr.

The rubber composition further includes an aromatic carboxylic acid or aromatic acid anhydride. Suitable aromatic carboxylic acids include but are not limited to benzoic acid and hydroxybenzoic acids, such as 2-hydroxybenzoic acid (salicylic acid), 3-hydroxybenzoic acid, and 4-hydroxybenzoic acid, substituted versions thereof, and the like. Suitable aromatic acid anyhydrides include phthalic anhydride, benzoic anhydride, substituted versions thereof, and the like.

Aromatic carboxylic acid or aromatic acid anhydride may be used in an amount ranging from 0.1 to 10 phr. In one embodiment, the Aromatic carboxylic acid or aromatic acid anhydride is used in an amount ranging from 0.1 to 5 phr. In one embodiment, the Aromatic carboxylic acid or aromatic acid anhydride is used in an amount ranging from 0.1 to 2 phr.

In one embodiment, the aromatic carboxylic acid or aromatic acid anhydride may be used in an amount greater than, or in excess of, that used for the polymeric amine. In one embodiment, the weight ratio aromatic carboxylic acid or aromatic acid anhydride to polymeric amine is at least 1. In one embodiment, the weight ratio aromatic carboxylic acid or aromatic acid anhydride to polymeric amine is at least 2. In one embodiment, the weight ratio aromatic carboxylic acid or aromatic acid anhydride to polymeric amine is at least 3.

The rubber composition may optionally include, in addition to the functionalized polymer, one or more rubbers or elastomers containing olefinic unsaturation. The phrases “rubber or elastomer containing olefinic unsaturation” or “diene based elastomer” are intended to include both natural rubber and its various raw and reclaim forms as well as various synthetic rubbers. In the description of this invention, the terms “rubber” and “elastomer” may be used interchangeably, unless otherwise prescribed. The terms “rubber composition,” “compounded rubber” and “rubber compound” are used interchangeably to refer to rubber which has been blended or mixed with various ingredients and materials and such terms are well known to those having skill in the rubber mixing or rubber compounding art. Representative synthetic polymers are the homopolymerization products of butadiene and its homologues and derivatives, for example, methylbutadiene, dimethylbutadiene and pentadiene as well as copolymers such as those formed from butadiene or its homologues or derivatives with other unsaturated monomers. Among the latter are acetylenes, for example, vinyl acetylene; olefins, for example, isobutylene, which copolymerizes with isoprene to form butyl rubber; vinyl compounds, for example, acrylic acid, acrylonitrile (which polymerize with butadiene to form NBR), methacrylic acid and styrene, the latter compound polymerizing with butadiene to form SBR, as well as vinyl esters and various unsaturated aldehydes, ketones and ethers, e.g., acrolein, methyl isopropenyl ketone and vinylethyl ether. Specific examples of synthetic rubbers include neoprene (polychloroprene), polybutadiene (including cis-1,4-polybutadiene), polyisoprene (including cis-1,4-polyisoprene), butyl rubber, halobutyl rubber such as chlorobutyl rubber or bromobutyl rubber, styrene/isoprene/butadiene rubber, copolymers of 1,3-butadiene or isoprene with monomers such as styrene, acrylonitrile and methyl methacrylate, as well as ethylene/propylene terpolymers, also known as ethylene/propylene/diene monomer (EPDM), and in particular, ethylene/propylene/dicyclopentadiene terpolymers. Additional examples of rubbers which may be used include alkoxy-silyl end functionalized solution polymerized polymers (SBR, PBR, IBR and SIBR), silicon-coupled and tin-coupled star-branched polymers. The preferred rubber or elastomers are polyisoprene (natural or synthetic), polybutadiene and SBR.

In one aspect the at least one additional rubber is preferably of at least two of diene based rubbers. For example, a combination of two or more rubbers is preferred such as cis 1,4-polyisoprene rubber (natural or synthetic, although natural is preferred), 3,4-polyisoprene rubber, styrene/isoprene/butadiene rubber, emulsion and solution polymerization derived styrene/butadiene rubbers, cis 1,4-polybutadiene rubbers and emulsion polymerization prepared butadiene/acrylonitrile copolymers.

In one aspect of this invention, an emulsion polymerization derived styrene/butadiene (E-SBR) might be used having a relatively conventional styrene content of about 20 to about 28 percent bound styrene or, for some applications, an E-SBR having a medium to relatively high bound styrene content, namely, a bound styrene content of about 30 to about 45 percent.

By emulsion polymerization prepared E-SBR, it is meant that styrene and 1,3-butadiene are copolymerized as an aqueous emulsion. Such are well known to those skilled in such art. The bound styrene content can vary, for example, from about 5 to about 50 percent. In one aspect, the E-SBR may also contain acrylonitrile to form a terpolymer rubber, as E-SBAR, in amounts, for example, of about 2 to about 30 weight percent bound acrylonitrile in the terpolymer.

Emulsion polymerization prepared styrene/butadiene/acrylonitrile copolymer rubbers containing about 2 to about 40 weight percent bound acrylonitrile in the copolymer are also contemplated as diene based rubbers for use in this invention.

The solution polymerization prepared SBR (S-SBR) typically has a bound styrene content in a range of about 5 to about 50, preferably about 9 to about 36, percent. The S-SBR can be conveniently prepared, for example, by organo lithium catalyzation in the presence of an organic hydrocarbon solvent.

In one embodiment, cis 1,4-polybutadiene rubber (BR) may be used. Such BR can be prepared, for example, by organic solution polymerization of 1,3-butadiene. The BR may be conveniently characterized, for example, by having at least a 90 percent cis 1,4-content.

The cis 1,4-polyisoprene and cis 1,4-polyisoprene natural rubber are well known to those having skill in the rubber art.

In one embodiment, the rubber composition may include from 10 to 90 phr of the functionalized elastomer, and from 90 to 10 phr of addtional rubbers or elastomers containing olefinic unsaturation

The term “phr” as used herein, and according to conventional practice, refers to “parts by weight of a respective material per 100 parts by weight of rubber, or elastomer.”

The rubber composition may also include up to 70 phr of processing oil. Processing oil may be included in the rubber composition as extending oil typically used to extend elastomers. Processing oil may also be included in the rubber composition by addition of the oil directly during rubber compounding. The processing oil used may include both extending oil present in the elastomers, and process oil added during compounding. Suitable process oils include various oils as are known in the art, including aromatic, paraffinic, naphthenic, vegetable oils, and low PCA oils, such as MES, TDAE, SRAE and heavy naphthenic oils. Suitable low PCA oils include those having a polycyclic aromatic content of less than 3 percent by weight as determined by the IP346 method. Procedures for the IP346 method may be found in Standard Methods for Analysis & Testing of Petroleum and Related Products and British Standard 2000 Parts, 2003, 62nd edition, published by the Institute of Petroleum, United Kingdom.

The rubber composition may include from about 10 to about 150 phr of silica. In another embodiment, from 20 to 80 phr of silica may be used.

The commonly employed siliceous pigments which may be used in the rubber compound include conventional pyrogenic and precipitated siliceous pigments (silica). In one embodiment, precipitated silica is used. The conventional siliceous pigments employed in this invention are precipitated silicas such as, for example, those obtained by the acidification of a soluble silicate, e.g., sodium silicate.

Such conventional silicas might be characterized, for example, by having a BET surface area, as measured using nitrogen gas. In one embodiment, the BET surface area may be in the range of about 40 to about 600 square meters per gram. In another embodiment, the BET surface area may be in a range of about 80 to about 300 square meters per gram. The BET method of measuring surface area is described in the Journal of the American Chemical Society, Volume 60, Page 304 (1930).

The conventional silica may also be characterized by having a dibutylphthalate (DBP) absorption value in a range of about 100 to about 400, alternatively about 150 to about 300.

The conventional silica might be expected to have an average ultimate particle size, for example, in the range of 0.01 to 0.05 micron as determined by the electron microscope, although the silica particles may be even smaller, or possibly larger, in size.

Various commercially available silicas may be used, such as, only for example herein, and without limitation, silicas commercially available from PPG Industries under the Hi-Sil trademark with designations 210, 243, etc; silicas available from Rhodia, with, for example, designations of Z1165MP and Z165GR and silicas available from Degussa AG with, for example, designations VN2 and VN3, etc.

Commonly employed carbon blacks can be used as a conventional filler in an amount ranging from 10 to 150 phr. In another embodiment, from 20 to 80 phr of carbon black may be used. Representative examples of such carbon blacks include N110, N121, N134, N220, N231, N234, N242, N293, N299, N315, N326, N330, N332, N339, N343, N347, N351, N358, N375, N539, N550, N582, N630, N642, N650, N683, N754, N762, N765, N774, N787, N907, N908, N990 and N991. These carbon blacks have iodine absorptions ranging from 9 to 145 g/kg and DBP number ranging from 34 to 150 cm³/100 g.

Other fillers may be used in the rubber composition including, but not limited to, particulate fillers including ultra high molecular weight polyethylene (UHMWPE), crosslinked particulate polymer gels including but not limited to those disclosed in U.S. Pat. Nos. 6,242,534; 6,207,757; 6,133,364; 6,372,857; 5,395,891; or 6,127,488, and plasticized starch composite filler including but not limited to that disclosed in U.S. Pat. No. 5,672,639. Such other fillers may be used in an amount ranging from 1 to 30 phr.

In one embodiment the rubber composition may contain a conventional sulfur containing organosilicon compound. In one embodiment, the sulfur containing organosilicon compounds are the 3,3′-bis(trimethoxy or triethoxy silylpropyl) polysulfides. In one embodiment, the sulfur containing organosilicon compounds are 3,3′-bis(triethoxysilylpropyl) disulfide and/or 3,3′-bis(triethoxysilylpropyl) tetrasulfide.

In another embodiment, suitable sulfur containing organosilicon compounds include compounds disclosed in U.S. Pat. No. 6,608,125. In one embodiment, the sulfur containing organosilicon compounds includes 3-(octanoylthio)-1-propyltriethoxysilane, CH₃(CH₂)₆C(═O)—S—CH₂CH₂CH₂Si(OCH₂CH₃)₃, which is available commercially as NXT™ from Momentive Performance Materials.

In another embodiment, suitable sulfur containing organosilicon compounds include those disclosed in U.S. Patent Publication No. 2003/0130535. In one embodiment, the sulfur containing organosilicon compound is Si-363 from Degussa.

The amount of the sulfur containing organosilicon compound in a rubber composition will vary depending on the level of other additives that are used. Generally speaking, the amount of the compound will range from 0.5 to 20 phr. In one embodiment, the amount will range from 1 to 10 phr.

It is readily understood by those having skill in the art that the rubber composition would be compounded by methods generally known in the rubber compounding art, such as mixing the various sulfur-vulcanizable constituent rubbers with various commonly used additive materials such as, for example, sulfur donors, curing aids, such as activators and retarders and processing additives, such as oils, resins including tackifying resins and plasticizers, fillers, pigments, fatty acid, zinc oxide, waxes, antioxidants and antiozonants and peptizing agents. As known to those skilled in the art, depending on the intended use of the sulfur vulcanizable and sulfur-vulcanized material (rubbers), the additives mentioned above are selected and commonly used in conventional amounts. Representative examples of sulfur donors include elemental sulfur (free sulfur), an amine disulfide, polymeric polysulfide and sulfur olefin adducts. In one embodiment, the sulfur-vulcanizing agent is elemental sulfur. The sulfur-vulcanizing agent may be used in an amount ranging from 0.5 to 8 phr, alternatively with a range of from 1.5 to 6 phr. Typical amounts of tackifier resins, if used, comprise about 0.5 to about 10 phr, usually about 1 to about 5 phr. Typical amounts of processing aids comprise about 1 to about 50 phr. Typical amounts of antioxidants comprise about 1 to about 5 phr. Representative antioxidants may be, for example, diphenyl-p-phenylenediamine and others, such as, for example, those disclosed in The Vanderbilt Rubber Handbook (1978), Pages 344 through 346. Typical amounts of antiozonants comprise about 1 to 5 phr. Typical amounts of fatty acids, if used, which can include stearic acid comprise about 0.5 to about 3 phr. Typical amounts of zinc oxide comprise about 2 to about 5 phr. Typical amounts of waxes comprise about 1 to about 5 phr. Often microcrystalline waxes are used. Typical amounts of peptizers comprise about 0.1 to about 1 phr. Typical peptizers may be, for example, pentachlorothiophenol and dibenzamidodiphenyl disulfide.

Accelerators are used to control the time and/or temperature required for vulcanization and to improve the properties of the vulcanizate. In one embodiment, a single accelerator system may be used, i.e., primary accelerator. The primary accelerator(s) may be used in total amounts ranging from about 0.5 to about 4, alternatively about 0.8 to about 1.5, phr. In another embodiment, combinations of a primary and a secondary accelerator might be used with the secondary accelerator being used in smaller amounts, such as from about 0.05 to about 3 phr, in order to activate and to improve the properties of the vulcanizate. Combinations of these accelerators might be expected to produce a synergistic effect on the final properties and are somewhat better than those produced by use of either accelerator alone. In addition, delayed action accelerators may be used which are not affected by normal processing temperatures but produce a satisfactory cure at ordinary vulcanization temperatures. Vulcanization retarders might also be used. Suitable types of accelerators that may be used in the present invention are amines, disulfides, guanidines, thioureas, thiazoles, thiurams, sulfenamides, dithiocarbamates and xanthates. In one embodiment, the primary accelerator is a sulfenamide If a second accelerator is used, the secondary accelerator may be a guanidine, dithiocarbamate or thiuram compound.

The mixing of the rubber composition can be accomplished by methods known to those having skill in the rubber mixing art. For example, the ingredients are typically mixed in at least two stages, namely, at least one non-productive stage followed by a productive mix stage. The final curatives including sulfur-vulcanizing agents are typically mixed in the final stage which is conventionally called the “productive” mix stage in which the mixing typically occurs at a temperature, or ultimate temperature, lower than the mix temperature(s) than the preceding non-productive mix stage(s). The terms “non-productive” and “productive” mix stages are well known to those having skill in the rubber mixing art. The rubber composition may be subjected to a thermomechanical mixing step. The thermomechanical mixing step generally comprises a mechanical working in a mixer or extruder for a period of time suitable in order to produce a rubber temperature between 140° C. and 190° C. The appropriate duration of the thermomechanical working varies as a function of the operating conditions, and the volume and nature of the components. For example, the thermomechanical working may be from 1 to 20 minutes.

The rubber composition may be incorporated in a variety of rubber components of the tire. For example, the rubber component may be a tread (including tread cap and tread base), sidewall, apex, chafer, sidewall insert, wirecoat or innerliner. In one embodiment, the component is a tread.

The pneumatic tire of the present invention may be a race tire, passenger tire, aircraft tire, agricultural, earthmover, off-the-road, truck tire, and the like. In one embodiment, the tire is a passenger or truck tire. The tire may also be a radial or bias.

Vulcanization of the pneumatic tire of the present invention is generally carried out at conventional temperatures ranging from about 100° C. to 200° C. In one embodiment, the vulcanization is conducted at temperatures ranging from about 110° C. to 180° C. Any of the usual vulcanization processes may be used such as heating in a press or mold, heating with superheated steam or hot air. Such tires can be built, shaped, molded and cured by various methods which are known and will be readily apparent to those having skill in such art.

This invention is illustrated by the following examples that are merely for the purpose of illustration and are not to be regarded as limiting the scope of the invention or the manner in which it can be practiced. Unless specifically indicated otherwise, parts and percentages are given by weight.

EXAMPLE 1

In this example, the effect of compounding a polymeric amine and an aromatic acid with a functionalized styrene-butadiene rubber is illustrated. Styrene-butadiene rubber was synthesized and terminated with S-benzyl-S′-triethoxysilylpropyltrithiocarbonate as disclosed in US2013/0131263. The resulting functionalized SBR is referred to as a siloxy/trithiocarbonate functionalized SBR.

Rubber compounds were mixed in a laboratory mixer in a multi-step mixing process following the recipe given in Table 1 (all amounts in phr). Polyethyleneimine (PEI) was added in either a first or a second non-productive mix step, as indicated in Table 2. An equal amount by weight of salicylic acid (i.e. salicylic acid/polyethyleneimine=1) was added to all compounds during the productive mix step. All compounds further included standard amounts of compounding additives, such as oils, waxes, antidegradants, and curatives.

Three series of rubber compounds were mixed accordingly. Series A included a control, non-functionalized styrene-butadiene rubber made via solution polymerization with alcohol termination. Series B included a comparative siloxy/thiol functionalized styrene-butadiene rubber (sulfanylsilane functionalized solution polymerized styrene-butadiene rubber, available commercially as Sprintan® SLR 4602, from Styron). Series C included the siloxy/trithiocarbonate functionalized SBR. Each of the three series A, B and C included five samples as indicated in Table 2, using elastomers as indicated in Table 3.

The mixed compounds were tested for viscoelastic properties with results given in Table 4. Tan delta as indicated was determined using using an Alpha Technologies Rubber Process Analyzer (RPA). A description of the RPA 2000, its capability, sample preparation, tests and subtests can be found in these references. H A Pawlowski and J S Dick, Rubber World, June 1992; J S Dick and H A Pawlowski, Rubber World, January 1997; and J S Dick and J A Pawlowski, Rubber & Plastics News, Apr. 26 and May 10, 1993.

Tan delta was determined for each sample at three different conditions as shown in Table 4. A rolling resistance index was defined as the ratio of the tan delta of a sample containing PEI to the tan delta of the sample 0 compound (no added PEI) for the given series, and averaged over the three tan delta measurements for each sample. By this method, a higher rolling resistance index is an indicator of better performance as a tire compound.

TABLE 1 Styrene-Butadiene 70 Polybutadiene 30 Silica 65 Polyethyleneimine (PEI) 0.4 or 0.75 as in Table 2

TABLE 2 Series Sample No. PEI addition step Polyethyleneimine, phr 0 None 0 1 Non-Productive (NP) 1 0.4 2 Non-Productive (NP) 2 0.4 3 Non-Productive (NP) 1 0.75 4 Non-Productive (NP) 2 0.75

TABLE 3 Series Styrene type A Control: Non-functionalized SBR B Comparative: Siloxy/Thiol functionalized SBR C Inventive: Siloxy/trithiocarbonate functionalized SBR

The rolling resistance index from Table 4 is shown graphically in FIG. 1, with error bars indicating±one standard deviation. As seen in FIG. 1, the combinate of polyethyleneimine and salicylic acid with the siloxy/trithiocarbonate functionalized SBR leads unexpectedly to a significantly better rolling resistance than the control and comparative samples. The rolling resistance performance of the siloxy/trithiocarbonate functionalized SBR is significantly better than might be expected simply due to enhancement of polymer/filler interaction by the polyethyleneimine and/or cleavage of the thiol ester in the trithiocarbonate group.

TABLE 4 Series Sample No. 0 1 2 3 4 PEI, phr 0 0.4 0.4 0.75 0.75 NP Step Added — 1 2 1 2 Series A: Non Functionalized SBR (Control) Tan Delta¹ 0.189 0.167 0.177 0.166 0.167 Tan Delta² 0.16 0.144 0.151 0.141 0.145 Tan Delta³ 0.137 0.122 0.127 0.128 0.137 RR Index 1 1.12 1.07 1.11 1.08 Stand. Dev. — 0.01 0.01 0.04 0.07 Series B: Siloxy/Thiol functionalized SBR (Comparative) Tan Delta¹ 0.143 0.135 0.129 0.134 0.128 Tan Delta² 0.117 0.109 0.106 0.11 0.106 Tan Delta³ 0.111 0.103 0.101 0.108 0.11 RR Index 1 1.07 1.10 1.05 1.08 Stand. Dev. — 0.01 0.00 0.02 0.06 Series C: Blocked trithiocarbonate functionalized SBR (Invention) Tan Delta¹ 0.18 0.145 0.143 0.141 0.136 Tan Delta² 0.149 0.122 0.117 0.121 0.115 Tan Delta³ 0.13 0.113 0.118 0.118 0.123 RR Index 1 1.20 1.21 1.20 1.23 Stand. Dev. — 0.05 0.10 0.09 0.15 ¹Measured at 5% strain, 30° C. ²Measured at 5% strain, 60° C. ³Measured at 10% strain, 100° C., 11 Hz

While certain representative embodiments and details have been shown for the purpose of illustrating the subject invention, it will be apparent to those skilled in this art that various changes and modifications can be made therein without departing from the scope of the subject invention. 

What is claimed is:
 1. A vulcanizable rubber composition comprising: (A) a functionalized elastomer comprising the reaction product of a living anionic elastomeric polymer and a polymerization terminator of formula I

where R¹, R² and R³ are independently C1 to C8 alkyl or C1 to C8 alkoxy, with the proviso that at least two of R¹, R² and R³ are C1 to C8 alkoxy; R⁴ is C1 to C8 alkyl; Si is silicon; S is sulfur; and Z is R⁵ or of formula II

where R⁵ is alkyl, aryl, alkylaryl or arylalkyl; (B) a polymeric amine comprising a primary amine functionality; and (C) an aromatic carboxylic acid or aromatic acid anhydride.
 2. The vulcanizable rubber composition of claim 1, wherein the polymerization terminator of formula I has the structure

where Et is ethyl.
 3. The vulcanizable rubber composition of claim 1, wherein the polymerization terminator of formula I is S-benzyl-S′-triethoxysilylpropyltrithiocarbonate.
 4. The vulcanizable rubber composition of claim 1, wherein the polymeric amine is a polyethyleneimine.
 5. The vulcanizable rubber composition of claim 1, wherein the polymeric amine is a polyoxyalkylene amine.
 6. The vulcanizable rubber composition of claim 1, wherein the amount of polymeric amine ranges from 0.1 to 10 phr.
 7. The vulcanizable rubber composition of claim 1, wherein the aromatic carboxylic acid or aromatic acid anhydride is selected from the group consisting of benzoic acid, salicylic acid, 3-hydroxybenzoic acid, 4-hydroxybenzoic acid, phthalic anhydride, and benzoic anhydride.
 8. The vulcanizable rubber composition of claim 1, wherein the amount of aromatic carboxylic acid or aromatic acid anhydride ranges from 0.1 to 10 phr.
 9. The vulcanizable rubber composition of claim 1, further comprising silica.
 10. A pneumatic tire comprising the vulcanizable rubber composition of claim
 1. 